I would go with the US Open. The Masters gets the big hype on TV so many golfers think it's the best. I like the US Open because it allows the average Joe to bust his butt and play with the Big Boys. Here is how you have to qualify for the Maters:
• Masters Tournament Champions (Lifetime)
• US Open Champions (Honorary, non-competing after 5 years)
• British Open Champions (Honorary, non-competing after 5 years)
• PGA Champions (Honorary,...

I have now used FunGolf for about six months and love it. The yardage is spot on and I have compared it to my playing partners GPS units and have found no discrepancy to other, more expensive units and apps. It keeps my score and statistics if I want plus other great features. It's free but I upgraded for $19.99 and do not regret it.

I am also looking for a good app for my IPhone 5S and am seriously looking at FunGolf. You can try it for free for a trial and pay $19.99 one time if you like it. No additional costs after that. It has a 3D screen shot which is unique and loaded with a bunch of extra features. I have contacted them with some questions and they seem pretty friendly and responsive. You can take a look at it on there website www.fungolf.com.